Jimmy,
I do this on a regular basis in my job building glass aquariumalthough i have specifically designed machinery here's the way i do it on site , purchase a diamond drill from ebay and with the tecnique put the tank/piece of glass on a table with a piece of foam under it use a second piece of foam and run diamond drill through it giving you a guide.....make sure you tank/glass will not spin on table generally the foam prevents this....now get a coke bottle and put a nail through the lid and pull nail out giving you a squirty bottle lol .....mark hole and place guide in position hold it down with one hand with the other drill slowly and have a 2nd person every few seconds squirt a few mls of water on the diamond drill...once you have drilled a couple millimetres into the glass remove giude and drill slowly always squirting water on it ....be sure not to apply to much pressure.
Feell free to message me if you would like more info......